An enclosure, such as a building entrance protector (BEP) enclosure, has a base, a mid layer pivotally connected to the base, and a cover pivotally connected to the mid layer. A mounting plane mounted to the mid layer divides the enclosure into two chambers--an inner chamber and an outer chamber. The mid layer provides at least two different mounting positions for the mounting plane, in order to provide different sets of volumes for the two chambers. In particular, by moving the mounting plane from the lower mounting position to the upper mounting position, the volume of the inner chamber is increased, while the volume of the outer chamber is decreased. The enclosure is designed such that the mounting plane can be reconfigured from one mounting position to the other in the field and without disturbing any of the hardware, including any electrical connections, housed within the two chambers, including any hardware mounted directly to the mounting plane. As such, the volumes of the chambers in the enclosure can be efficiently changed in the field as needed to accommodate changing hardware needs.